Add local PackageManager instance in PhoneWindowManager.

There are multiple calls relying on PackageManager methods
through Context#getPackageManager outside of init() now.
Replace these with calls through a local instance.

Bug: 140787161
Test: presubmit
Change-Id: If793434a0edfd7b33c22e79ce343eac3a1156f0f
Signed-off-by: Julius D'souza <jdsouza@google.com>